1. Field of the Invention
The present invention relates to a process and apparatus for recovering a lower alcohol from a mixture thereof with water. Particularly, the present invention relates to a process and apparatus for recovering a lower alcohol from a mixture thereof with water, derived from a vapor drying process for water-washed articles, for example, precision electronic components such as printed circuit boards, semiconductor wafers and electronic parts; and lenses. More particularly, the present invention relates to a process and apparatus for separating and recovering a lower alcohol from a mixed liquid thereof with water derived from a process in which a vapor of a lower alcohol is brought into contact with at least one article, for example, a precision electronic component, for a vapor drying of the article and the resultant mixed liquid of the lower alcohol with water is subjected to a vaporizing step and then to a gas-separating step in which the water vapor is separated by a gas-separating membrane to recover the lower alcohol at a high concentration.
2. Description of the Related Arts
It is known that certain water-wetted articles can be safely dried only by bringing the article into contact with a high temperature vapor of a volatile solvent, for example, isopropyl alcohol, generated by heating the solvent. This vapor drying process is disclosed, for example, by Japanese Unexamined Patent Publication No. 56-168072. Also, an apparatus for the vapor drying process is disclosed, for example, in Japanese Unexamined Patent Publication No. 58-207638.
The conventional vapor drying apparatus is provided with a region for generating a vapor of a treating liquid, for example, a lower alcohol, a region for treating at least one water-wetted article to be vapor dried, and a region for collecting the used treating liquid contaminated with water derived from the water-wetted article. To regenerate the treating liquid containing water collected in the collecting region, a refining apparatus provided with a means for removing water from the used treating liquid containing water, and with a vaporizing means, is connected to the collecting region for the used treating liquid.
Japanese Unexamined Patent Publication No. 62-106,630 discloses a vapor drying apparatus capable of introducing the resultant refined treating liquid to the vapor-generating region. This Japanese publication also discloses that the water-containing treating liquid derived from the vapor drying region in which a water-wetted article, for example, a semiconductor wafer, is dried with a vapor of a lower alcohol, is refined by a refining apparatus having a water-removing means and a distilling means, and the refined treating liquid is returned to the vapor-generating region to be reused as the treating liquid.
In the conventional vapor drying apparatus, however, the means for removing water from the water-containing treating liquid is not specifically disclosed but is considered to utilize a desiccant as a means for removing water from the water-containing treating liquid. In this case, there is a limitation to the treating capacity of the desiccant, and a reclaiming of the used desiccant becomes necessary.
Further, the above-mentioned conventional vapor-drying apparatus is disadvantageous in that the content of water in the used treating liquid, for example, lower alcohol, collected in a bottom portion of a vapor treating vessel is gradually increased, and finally, it become impossible to generate a vapor comprising the lower alcohol in a satisfactorily high concentration, and thus it is no longer effective for the vapor drying of the water-wetted articles from the collected treating liquid, due to a high concentration of water in the collected treating liquid. Therefore, fresh high purity lower alcohol must be successively supplied to the vapor drying apparatus and the used treating liquid containing water in an increased concentration must be continuously discharged from the vapor drying apparatus. Therefore, a practical economic and effective process for reclaiming the discharged water-containing treating liquid is not known.